The "strength" or "weakness" of dough is an important aspect of baking. Flours with a low protein content are customarily characterized as "weak"; the gluten (the cohesive, extensible, rubbery mass which is formed by mixing flour and water) formed with weak flour will be very extensible under stress, but will not return to its original dimensions when the stress is removed. Flours with a high protein content are customarily characterized as "strong" and the gluten formed with strong flour will be less extensible than a weak flour, and stress which is applied during mixing will be restored without breakdown to a greater extent than a weak flour. Strong dough is generally preferred in most baking contexts because of the superior rheological and handling properties of the dough and the superior form and texture qualities of the final baked product made from the dough.
For example, stronger dough is generally more stable; the stability of dough is one of the most important (if not the most important) characteristics of baking dough.
American Association of Cereal Chemists Method 36-01A defines dough stability as "(a) the range of dough time over which a positive Response is obtained; and (b) that property of a rounded dough by which it resists flattening under its own weight over a course of time." Response is defined, by the same Method, as "the reaction of dough to a known and specific stimulus, substance or set of conditions, usually determined by baking it in comparison with a control."
Stable dough is particularly useful in large scale applications where it may be difficult to control all processing parameters; strong dough will exhibit a greater tolerance of, e.g. mixing time and proofing time, and still result in quality products. Less stable dough will exhibit less tolerance in this regard. Dough stability is also extremely important in retarded fermentation and frozen dough baking. Weakening of the dough in these contexts decreases the loaf volume of the bread and has other deleterious effects.
Bakers have long used dough "conditioners" to strengthen the dough. It is suggested that such conditioners, which consist primarily of non-specific oxidants such as bromates, peroxides, iodates and ascorbic acid, help form inter-protein bonds which strengthen the dough. However, non-specific oxidants have numerous drawbacks; in particular, they can have a negative effect on the organoleptic qualities of the final product and are relatively expensive in commercial quantities and, in the case of bromates, are not permitted in certain countries.
The use of enzymes as dough conditioners has been considered as an alternative to the non-specific oxidants. In particular, glucose oxidase has been used--sometimes in combination with other conditioners--to condition or "mature" flour. U.S. Pat. No. 2,783,150 (Luther) discusses the treatment of flour with glucose oxidase which allegedly can be used to form an improved dough with better handling properties and a high quality final baked product. The effects of glucose oxidase are somewhat contradictory. Water absorption of the dough is increased and in some instances the use of glucose oxidase has resulted in some improved dough quality, albeit at high levels uneconomical for commercial purposes. However, glucose oxidase, in some contexts, may actually impair dough rheology and has never been successfully used, per se, as a dough conditioner on a commercial scale.
It has also been suggested that the enzyme, sulfhydryl oxidase, could be used to strengthen dough. Sulfhydryl oxidase ("SHX") catalyzes--in the presence of oxygen--the conversion of thiol compounds to their corresponding disulfides according to the equation: EQU 2RSH+O.sub.2 .fwdarw.RSSR+H.sub.2 O.sub.2
The role played by sulfur containing reactive groups in wheat protein has not been fully defined but it is suggested that the reaction of free sulfhydryl groups to form disulfide bonds has an important role in the mixing and strength of dough. In particular, if disulfide bonds are formed between two protein chains, the resulting cross-linking of chains could strengthen the dough. Hence, SHX could be expected to strengthen dough by catalyzing the reaction of free sulfhydryl groups into inter-protein disulfide bonds.
However, Kaufmann et al., Cereal Chemistry, Vol. 64:3 (1987), evaluated bovine SHX's ability to strengthen wheat dough and concluded that it did not have any strengthening effect. The baking tests reported by Kaufmann et al. did not show any "noticeable" effect of SHX on loaf volume, and mixograph studies on SHX treated dough which did not show any "noticeable" effect on the time to reach a mixing peak or the extent of dough breakdown. Kaufmann et al also evaluated the effect of SHX on flour/buffer suspensions and concluded that SHX did not show any effect on the free-SH groups of flour. Kaufmann et al state that--for a number of possible reasons--SHX was not able to catalyze formation of disulfide bonds in the systems tested.
Therefore, one would not expect a combination of glucose oxidase and SHX to have an appreciable effect on dough strength, or on the quality of the baked product. Surprisingly, it has now been discovered that an enzyme preparation which includes both glucose oxidase and microbial SHX will appreciably strengthen dough and improves the form and texture of the final baked product. This action takes place at levels of glucose oxidase and SHX which makes enzyme treatment economically feasible on a commercial scale. The use of this enzyme preparation is particularly effective in retarded baking and frozen dough contexts, when the actual baking does not take place immediately following dough preparation.